Made from metallophthalocyanine (light blue) and benzothiadiazole blocks (purple), this framework compound facilitates high electron mobility.

Credit: J. Am. Chem. Soc.

Made from metallophthalocyanine (light blue) and benzothiadiazole blocks (purple), this framework compound facilitates high electron mobility.

Credit: J. Am. Chem. Soc.

A covalent organic framework (COF) compound composed of sheets of metallo­phthalocyanine units connected by electron-deficient organic groups readily transports electrons—negative, or n-type, charge carriers—according to researchers in Japan and Thailand (J. Am. Chem. Soc., DOI: 10.1021/ja2052396). Other examples of COFs featuring two-dimensional polymeric layers have been reported, but all of those compounds are p-type conductors. Framework compounds are porous crystalline substances that have been widely studied for industrial applications in gas storage and catalysis. Because of the arrangement of aromatic groups and associated charge-conducting π electron orbitals in some of these compounds, COFs also hold promise for molecular electronics, photovoltaics, and other applications driven by charge conduction. Yet such applications require a combination of p-type and n-type conductivity. In an advance that moves COFs in that direction, Xuesong Ding, Long Chen, and Donglin Jiang of Japan’s Institute for Molecular Science, in Okazaki, and coworkers cocondensed nickel phthalocyanine (NiPc) and an electron-deficient benzothiadiazole derivative. Comparison tests show that in contrast to p-type conduction mediated by a related NiPc-based COF that lacks electron-deficient groups, including them in the new COF switches the mode of conduction to n-type.